Add custom-size QR code download on ad detail page (v2.3.135)

Admins can now enter a width in cm, see the computed pixel size at 300 DPI,
and download a crisp upscaled QR code PNG for print materials. Uses
ImageMagick nearest-neighbor interpolation to preserve sharp QR edges.
Also fixes pre-existing credo nesting warning in maybe_regenerate_qr_code.

Author: wintermeyer

lib/animina/ads/qr_code.ex

@@ -43,6 +43,28 @@ defmodule Animina.Ads.QrCode do
     end
   end
 
+  @doc """
+  Resizes a QR code PNG to the given pixel size using nearest-neighbor
+  interpolation (crisp edges). Returns `{:ok, tmp_path}` or `{:error, reason}`.
+  """
+  def resize(source_path, pixel_size) when is_integer(pixel_size) and pixel_size > 0 do
+    with :ok <- check_dependencies() do
+      tmp_path =
+        Path.join(
+          System.tmp_dir!(),
+          "qr_resized_#{pixel_size}_#{System.unique_integer([:positive])}.png"
+        )
+
+      size_str = "#{pixel_size}x#{pixel_size}"
+      {cmd, args} = magick_cmd([source_path, "-filter", "point", "-resize", size_str, tmp_path])
+
+      case System.cmd(cmd, args, stderr_to_stdout: true) do
+        {_, 0} -> {:ok, tmp_path}
+        {err, _} -> {:error, "ImageMagick resize failed: #{err}"}
+      end
+    end
+  end
+
   @doc """
   Generates a QR code PNG for the given ad.
 

lib/animina_web/controllers/ad_qr_controller.ex

@@ -6,6 +6,7 @@ defmodule AniminaWeb.AdQrController do
   use AniminaWeb, :controller
 
   alias Animina.Ads
+  alias Animina.Ads.QrCode
 
   def download(conn, %{"id" => id}) do
     case Ads.get_ad(id) do
@@ -27,6 +28,41 @@ defmodule AniminaWeb.AdQrController do
     end
   end
 
+  def download_sized(conn, %{"id" => id, "size" => size_str}) do
+    with {size, ""} <- Integer.parse(size_str),
+         true <- size >= 100 and size <= 10_000,
+         %{qr_code_path: path} when is_binary(path) <- Ads.get_ad(id),
+         true <- File.exists?(path),
+         {:ok, tmp_path} <- QrCode.resize(path, size) do
+      conn =
+        conn
+        |> put_resp_header("content-type", "image/png")
+        |> put_resp_header(
+          "content-disposition",
+          "attachment; filename=\"qr_#{size}x#{size}.png\""
+        )
+        |> send_file(200, tmp_path)
+
+      File.rm(tmp_path)
+      conn
+    else
+      false ->
+        conn |> put_status(:not_found) |> text("QR code file not found")
+
+      nil ->
+        conn |> put_status(:not_found) |> text("Not found")
+
+      %{qr_code_path: _} ->
+        conn |> put_status(:not_found) |> text("Not found")
+
+      {:error, reason} ->
+        conn |> put_status(:unprocessable_entity) |> text("Resize failed: #{reason}")
+
+      _ ->
+        conn |> put_status(:bad_request) |> text("Invalid size (must be 100–10000)")
+    end
+  end
+
   def show(conn, %{"id" => id}) do
     case Ads.get_ad(id) do
       %{qr_code_path: path} when is_binary(path) ->

lib/animina_web/live/admin/ad_detail_live.ex

@@ -6,6 +6,8 @@ defmodule AniminaWeb.Admin.AdDetailLive do
   alias Animina.Ads.QrCode
   alias AniminaWeb.Layouts
 
+  require Logger
+
   import AniminaWeb.Helpers.AdminHelpers, only: [parse_int: 2, format_datetime: 1]
 
   use AniminaWeb.Helpers.PaginationHelpers, filter_events: []
@@ -22,6 +24,11 @@ defmodule AniminaWeb.Admin.AdDetailLive do
          |> push_navigate(to: ~p"/admin/ads")}
 
       ad ->
+        ad = maybe_regenerate_qr_code(ad)
+
+        default_cm = 5.0
+        default_pixels = cm_to_pixels(default_cm)
+
         {:ok,
          socket
          |> assign(
@@ -34,7 +41,9 @@ defmodule AniminaWeb.Admin.AdDetailLive do
            daily_counts: Ads.daily_visit_counts(ad.id),
            os_breakdown: Ads.visit_breakdown(ad.id, :os),
            browser_breakdown: Ads.visit_breakdown(ad.id, :browser),
-           device_breakdown: Ads.visit_breakdown(ad.id, :device_type)
+           device_breakdown: Ads.visit_breakdown(ad.id, :device_type),
+           custom_cm: default_cm,
+           custom_pixels: default_pixels
          )
          |> stream(:visits, [])}
     end
@@ -81,6 +90,46 @@ defmodule AniminaWeb.Admin.AdDetailLive do
     end
   end
 
+  @impl true
+  def handle_event("update-qr-size", %{"cm" => cm_str}, socket) do
+    case Float.parse(cm_str) do
+      {cm, _} when cm >= 1.0 and cm <= 80.0 ->
+        {:noreply, assign(socket, custom_cm: cm, custom_pixels: cm_to_pixels(cm))}
+
+      _ ->
+        {:noreply, socket}
+    end
+  end
+
+  defp cm_to_pixels(cm), do: round(cm * 300 / 2.54)
+
+  defp maybe_regenerate_qr_code(%{qr_code_path: path} = ad)
+       when is_binary(path) and path != "" do
+    if File.exists?(path), do: ad, else: regenerate_qr_code(ad, path)
+  end
+
+  defp maybe_regenerate_qr_code(ad), do: ad
+
+  defp regenerate_qr_code(ad, path) do
+    Logger.warning("QR code file missing for ad ##{ad.number}, regenerating: #{path}")
+
+    with {:ok, new_path} <- QrCode.generate(ad),
+         {:ok, updated_ad} <- Ads.update_qr_code_path(ad, new_path) do
+      updated_ad
+    else
+      {:error, reason} ->
+        Logger.error("Failed to regenerate QR code for ad ##{ad.number}: #{inspect(reason)}")
+        clear_stale_qr_path(ad)
+    end
+  end
+
+  defp clear_stale_qr_path(ad) do
+    case Ads.update_qr_code_path(ad, nil) do
+      {:ok, cleared_ad} -> cleared_ad
+      _ -> ad
+    end
+  end
+
   defp build_path(socket, overrides) do
     ad = socket.assigns.ad
 
@@ -155,6 +204,29 @@ defmodule AniminaWeb.Admin.AdDetailLive do
                 <.icon name="hero-arrow-down-tray-mini" class="w-3 h-3" />
                 {gettext("Download QR")}
               </a>
+              <form phx-change="update-qr-size" class="mt-2 flex flex-col items-center gap-1">
+                <label class="text-xs text-base-content/50">{gettext("Width (cm)")}</label>
+                <input
+                  type="number"
+                  name="cm"
+                  value={@custom_cm}
+                  step="0.1"
+                  min="1"
+                  max="80"
+                  class="input input-xs input-bordered w-20 text-center"
+                />
+                <span class="text-xs text-base-content/50">
+                  {@custom_pixels} × {@custom_pixels} px
+                </span>
+                <a
+                  href={~p"/admin/ads/#{@ad.id}/qr-code/sized?size=#{@custom_pixels}"}
+                  class="btn btn-outline btn-xs"
+                  download
+                >
+                  <.icon name="hero-arrow-down-tray-mini" class="w-3 h-3" />
+                  {gettext("Download custom size")}
+                </a>
+              </form>
             </div>
             <div :if={!@ad.qr_code_path} class="flex flex-col items-center gap-2">
               <div class="w-32 h-32 bg-base-300 rounded flex items-center justify-center">

lib/animina_web/router.ex

@@ -190,6 +190,7 @@ defmodule AniminaWeb.Router do
     # Ad QR code serving (admin-only)
     get "/admin/ads/:id/qr-code", AdQrController, :download
     get "/admin/ads/:id/qr-code/show", AdQrController, :show
+    get "/admin/ads/:id/qr-code/sized", AdQrController, :download_sized
 
     post "/role/switch", RoleController, :switch
     post "/my/settings/update-password", UserSessionController, :update_password

mix.exs

@@ -4,7 +4,7 @@ defmodule Animina.MixProject do
   def project do
     [
       app: :animina,
-      version: "2.3.134",
+      version: "2.3.135",
       elixir: "~> 1.19",
       elixirc_paths: elixirc_paths(Mix.env()),
       start_permanent: Mix.env() == :prod,